1. Field of the Invention
The present invention relates generally to magnetic suspensions or levitations for movable members, movable in rotation about an axis or in extended linear translation. More particularly, the invention pertains to a novel magnetic and electromagnetic core, coil and electronic circuit configuration adaptable to rotational applications such as for suspending the spin axis of the rotor and gimbal axes of gyroscopic devices, or to translational applications such as for freely suspending vehicles relative to a track in mass transit systems.
2. Description of the Prior Art
Magnetic suspensions have been proposed and used extensively in the past for substantially frictionlessly suspending of a movable member, but in most cases the suspended member was of very low mass and moment of inertia, such as for example for suspending the rotor of a watt/hour meter, for suspending very light, hollow shell-like gyro rotors, or for assisting in the suspension of heavier objects such as fluid floated gyroscopes.
More recently, considerable investigative work has been done in developing magnetic bearing suspensions for much heavier objects, particularly in rotary applications such as in centrifuges and large gyroscopic rotors. Examples of the latter are disclosed in U.S. Pat. Nos. 3,428,371 and 3,473,852. More specifically, improvements in magnetic suspensions of the general type shown in these patents have been suggested, reference being particularly directed to the work of P. A. Studer as described by him in the NASA Goddard Space Flight Center report identified as NASA-TM-X-6611, dated January 1972, and entitled "Magnetic Bearings for Spacecraft". The present invention constitutes a significant improvement of the magnetic bearing disclosed in this report.
In general, and considering for this discussion the rotational application, the entire load of the suspended member is carried by magnetic fields across small gaps between the member and the fixed support member. In the case of spindle support, these gaps are arranged symmetrically at either end of the spindle supporting the rotating mass. The gaps may be configured such that radial loads are supported by the quiescent or fixed flux of a permanent magnet across the gap, and which may be referred to herein as a passive loop system, i.e., the tendency of attractive poles to align themselves to seek the minimum reluctance or maximum co-energy position, and the inherent instability of the attractive flux in the axial direction is overcome by a variable flux field, either across the same gap or further independent gaps, produced by electromagnetic means such as coils driven by a closed loop servo system responsive to the movement (position, rate, acceleration, or combinations thereof) between the supported and fixed members, and which may be referred to herein as an active loop. In some configurations, both the radial support flux and axial support flux across the same gaps are provided only by electromagnets as shown in the above-mentioned U.S. Pat. No. 3,473,852, while the above-mentioned U. S. Pat. No. 3,428,371 is illustrative of an axially/passive, radially/active configuration using separate gaps for each.
Studer discloses a radially passive/axially active configuration in which the permanent magnet flux is directed across circular axial gaps between soft iron cylindrical members to produce inherent radial stiffness while the electromagnetic coils of the axially active loop serve to produce a flux which modulates the permanent magnet flux. More specifically, and considering only one bearing assembly at one end of a support spindle or shaft, the Studer configuration comprises four axial gaps and three flux loops conducted by soft iron cylindrical members characterized by the fact that the active or modulating flux does not have to counter the reluctance of the permanent magnet, but rather has a preferred low-reluctance path through soft iron. The disadvantage of the Studer configuration, however, resides in the fact that two permanent magnets are required for the passive radial support and one common coil for the active axial support and that with this configuration only the flux in two of the four gaps is modulated, thereby reducing efficiency. Furthermore, the radial stiffness is fixed or uncontrollable. Also, the coil and magnets are not supported on a common element; one is mounted on the suspended element while the other is on the fixed element, or vice versa, thus adding mass to the supported element and/or requiring some kind of current conductor to the rotating member.